1. Field of the Invention
This invention relates to a character generator, and, more particularly, it is concerned with a character generator which increases the utility and efficiency of a pattern memory in storing character patterns therein.
2. Description of the Prior Art
There has so far been known a character generator which expresses character patterns with, for example, a dot matrix of 5 rows .times. 8 lines. The character patterns expressed by the 5.times.8 dot matrix are stored in an addressable memory, and can be called out from the memory by applying thereto an address signal to designate the desired character pattern. However, the character patterns thus stored in the memory are usually not output all at one time, but instead are output in several separate and distinct portions with the lines and rows of the dot matrix forming as a unit the entire character. For example, FIG. 1A of the accompanying drawing is a block diagram that explains a conventional character generator. In the drawing, a reference symbol CP designates a memory for storing character patterns therein, which selects one character pattern out of a plurality of character patterns stored therein in response to address signals AS3 to AS9 from address signal sources AL3 through AL9 CTN denotes a counter that designates a row (or column) of one character pattern thereby selecting a portion thereof. Here, the counter CTN is a quinary counter. The character address signal sources AL3 through Al9 select one of a plurality of character patterns out of the memory CP.
When the memory CP is accessed by the character address signal sources AL3 to AL9 and the counter CTN, the character patterns (A1 to A5, B1 to B5, P1 to P5 each representing one character pattern) should be disposed in the memory with a certain intervals among them as shown in FIG. 1B. Such necessity arises due to the fact that, while the addresses of the memory are all expressed in terms of a number of proceedings in computation, the counter CTN is just quinary. In more detail, while the quinary number can be expressed in three-bit, the octonary number can also be expressed in three-bit, on account of which there occurs a portion where no memory can be accessed by the counter CTN. Therefore, the character patterns should be arranged with certain intervals in the memory CP. In this regard, the address occupies a matrix of 8.times.8=64 bits, while it should primarily occupy a matrix of 5.times.8=40 bits for one character, causing a waste of 8.times.3=24 bits per one character. As the result, a memory having a capacity of 8,192 bits can only attain storage of 2.sup.7 .times.8.times.5=5120 bits which correspond to 128 characters, whereby considerable portions in the memory remain unused. Therefore its working efficiency is poor and uneconomical.